Trophoblast uptake of DBP regulates intracellular actin and promotes matrix invasion

Early pregnancy is characterised by elevated circulating levels of vitamin D binding protein (DBP). The impact of this on maternal and fetal health is unclear but DBP is present in the placenta, and DBP gene variants have been linked to malplacentation disorders such as preeclampsia. The functional role of DBP in the placenta was investigated using trophoblastic JEG3, BeWo and HTR8 cells. All three cell lines showed intracellular DBP with increased expression and nuclear localisation of DBP in cells treated with the active form of vitamin D, 1,25-dihydroxyvitamin D (1,25D). When cultured in the serum of mice lacking DBP (DBP-/-), JEG3 cells showed no intracellular DBP indicating uptake of exogenous DBP. Inhibition of the membrane receptor for DBP, megalin, also suppressed intracellular DBP. Elimination of intracellular DBP with DBP-/- serum or megalin inhibitor suppressed matrix invasion by trophoblast cells and was associated with increased nuclear accumulation of G-actin. Conversely, treatment with 1,25D enhanced matrix invasion. This was independent of the nuclear vitamin D receptor but was associated with enhanced ERK phosphorylation, and inhibition of ERK kinase suppressed trophoblast matrix invasion. When cultured with serum from pregnant women, trophoblast matrix invasion correlated with DBP concentration, and DBP was lower in first-trimester serum from women who later developed preeclampsia. These data show that the trophoblast matrix invasion involves uptake of serum DBP and associated intracellular actin-binding and homeostasis. DBP is a potential marker of placentation disorders such as preeclampsia and may also provide a therapeutic option for improved placenta and pregnancy health.

Vitamin D Binding Protein (VDBP) and Its Gene Polymorphisms-The Risk of Malignant Tumors and Other Diseases

Vitamin D is an important component of the endocrine system that controls calcium homeostasis and bone mineralization. Because of the very short half-life of free serum vitamin D it is stabilized and transported to target tissues by being bound to the vitamin D binding protein (VDBP). The most common polymorphisms: rs4588 and rs7041 in the vitamin D binding protein gene may correlate with differences in vitamin D status in the serum. This review presents data that relate to the presence of genetic variants in the VDBP gene in correlation with certain diseases, mostly concerning cancers (breast, prostate, pancreatic, lung, colorectal, basal cell carcinoma cancer and cutaneous melanoma) or other related diseases (thyroid autoimmunity disorders, obesity, diabetes mellitus, bone metabolism, rheumatoid arthritis, ankylosing spondylitis, asthma, chronic obstructive pulmonary disease, tuberculosis and coronary artery diseases).

Vitamin D binding protein: a multifunctional protein of clinical importance

Since the discovery of group-specific component and its polymorphism by Hirschfeld in 1959, research has put spotlight on this multifunctional transport protein (vitamin D binding protein, DBP). Besides the transport of vitamin D metabolites, DBP is a plasma glycoprotein with many important functions, including sequestration of actin, modulation of immune and inflammatory responses, binding of fatty acids, and control of bone development. A considerable DBP polymorphism has been described with a specific allele distribution in different geographic area. Multiple studies have shed light on the interesting relationship between polymorphisms of the DBP gene and the susceptibility to diseases. In this review, we give an overview of the multifunctional character of DBP and describe the clinical importance of DBP and its polymorphisms. Finally, we discuss the possibilities to use DBP as a novel therapeutic agent.

Vitamin D binding protein and monocyte response to 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D: analysis by mathematical modeling

Vitamin D binding protein (DBP) plays a key role in the bioavailability of active 1,25-dihydroxyvitamin D (1,25(OH)₂D) and its precursor 25-hydroxyvitamin D (25OHD), but accurate analysis of DBP-bound and free 25OHD and 1,25(OH)₂D is difficult. To address this, two new mathematical models were developed to estimate: 1) serum levels of free 25OHD/1,25(OH)₂D based on DBP concentration and genotype; 2) the impact of DBP on the biological activity of 25OHD/1,25(OH)₂D in vivo. The initial extracellular steady state (eSS) model predicted that 50 nM 25OHD and 100 pM 1,25(OH)₂D), <0.1% 25OHD and <1.5% 1,25(OH)₂D are ‘free’ in vivo. However, for any given concentration of total 25OHD, levels of free 25OHD are higher for low affinity versus high affinity forms of DBP. The eSS model was then combined with an intracellular (iSS) model that incorporated conversion of 25OHD to 1,25(OH)₂D via the enzyme CYP27B1, as well as binding of 1,25(OH)₂D to the vitamin D receptor (VDR). The iSS model was optimized to 25OHD/1,25(OH)₂D-mediated in vitro dose-responsive induction of the vitamin D target gene cathelicidin (CAMP) in human monocytes. The iSS model was then used to predict vitamin D activity in vivo (100% serum). The predicted induction of CAMP in vivo was minimal at basal settings but increased with enhanced expression of VDR (5-fold) and CYP27B1 (10-fold). Consistent with the eSS model, the iSS model predicted stronger responses to 25OHD for low affinity forms of DBP. Finally, the iSS model was used to compare the efficiency of endogenously synthesized versus exogenously added 1,25(OH)₂D. Data strongly support the endogenous model as the most viable mode for CAMP induction by vitamin D in vivo. These novel mathematical models underline the importance of DBP as a determinant of vitamin D ‘status’ in vivo, with future implications for clinical studies of vitamin D status and supplementation.

Vitamin D binding protein-macrophage activating factor directly inhibits proliferation, migration, and uPAR expression of prostate cancer cells

Background

Vitamin D binding protein-macrophage activating factor (DBP-maf) is a potent inhibitor of tumor growth. Its activity, however, has been attributed to indirect mechanisms such as boosting the immune response by activating macrophages and inhibiting the blood vessel growth necessary for the growth of tumors.

Methods and Findings

In this study we show for the first time that DBP-maf exhibits a direct and potent effect on prostate tumor cells in the absence of macrophages. DBP-maf demonstrated inhibitory activity in proliferation studies of both LNCaP and PC3 prostate cancer cell lines as well as metastatic clones of these cells. Flow cytometry studies with annexin V and propidium iodide showed that this inhibitory activity is not due to apoptosis or cell death. DBP-maf also had the ability to inhibit migration of prostate cancer cells in vitro. Finally, DBP-maf was shown to cause a reduction in urokinase plasminogen activator receptor (uPAR) expression in prostate tumor cells. There is evidence that activation of this receptor correlates with tumor metastasis.

Conclusions

These studies show strong inhibitory activity of DBP-maf on prostate tumor cells independent of its macrophage activation.

Gc-globulin in liver disease

This doctoral thesis is based on seven previously published papers and reports on the role of the actin-scavenger Gc-globulin in acute and chronic liver diseases. Gc-globulin is synthesized in the liver and is a multifunctional protein; however, its main physiologic function is presumably actin binding and actin scavenging. Actin is a major cellular protein released during cell necrosis that may cause fatal formation of actin-containing thrombi in the circulation if the actin scavenging capacity of Gc-globulin is exceeded. In my studies, I found serum Gc-globulin levels to be reduced in liver disease, most so in patients with acute liver failure (ALF). In patients admitted with acetaminophen (paracetamol) overdose, Gc-globulin concentrations were lower in patients with hepatic encephalopathy than in those without and the levels nadired at approximately 60-72 hours after acetaminophen ingestion, corresponding with the peak in aminotransferese levels (and thus, hepatic necrosis). In patients with ALF, admission Gc-globulin was significantly lower in 47 nonsurvivors than in 30 survivors, 26% and 46% of normal, respectively (P<0.001). The predictive value of outcome using a Gc-globulin cutoff level of 100 mg/L equaled that of the internationally accepted King's College Hospital criteria. The prognostic value of Gc-globulin was confirmed in a separate study including 106 patients from the United States with nonacetaminophen-induced ALF now using an automated nephelometric assay whereas the prognostic value seemed less obvious for acetaminophen-induced ALF. Multiple organ failure (MOF) is a frequent complication of ALF. In ALF patients with deep coma (hepatic encephalopathy grade III or IV) Gc-globulin levels correlated inversely with the number of failing organs. Levels were lower in patients who later developed MOF than in those who did not. Surprisingly, kinetic studies in patients with ALF and acute on chronic liver disease showed Gc-globulin production to be 7-fold increased in these conditions. Despite this increase Gc-globulin levels were severely reduced and the reduction must therefore be due to a highly increased consumption of Gc-globulin - probably because of hepatocyte necrosis and removal from the circulation of Gc-globulin:actin complexes or because of its role in immune-related functions. Patients with chronic liver disease had reduced Gc-globulin levels, but the reduction was less pronounced than in ALF. After liver transplantation, Gc-globulin concentrations normalized within two weeks, in contrast to the continuous decrease in albumin levels suggesting a very different regulation of these two phylogenetically related proteins. It remains to be studied if lack of Gc-globulin contributes to the pathogenesis of patients with ALF or chronic liver disease. Future studies should focus on the potential value of Gc-globulin substitution in these patients.

Vitamin D-binding protein influences total circulating levels of 1,25-dihydroxyvitamin D3 but does not directly modulate the bioactive levels of the hormone in vivo

Mice deficient in the expression of vitamin D-binding protein (DBP) are normocalcemic despite undetectable levels of circulating 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. We used this in vivo mouse model together with cells in culture to explore the impact of DBP on the biological activity of 1,25(OH)(2)D(3). Modest changes in the basal expression of genes involved in 1,25(OH)(2)D(3) metabolism and calcium homeostasis were observed in vivo; however, these changes seemed unlikely to explain the normal calcium balance seen in DBP-null mice. Further investigation revealed that despite the reduced blood levels of 1,25(OH)(2)D(3) in these mice, tissue concentrations were equivalent to those measured in wild-type counterparts. Thus, the presence of DBP has limited impact on the extracellular pool of 1,25(OH)(2)D(3) that is biologically active and that accumulates within target tissues. In cell culture, in contrast, the biological activity of 1,25(OH)(2)D(3) is significantly impacted by DBP. Here, although DBP deficiency had no effect on the activation profile itself, the absence of DBP strongly reduced the concentration of exogenous 1,25(OH)(2)D(3) necessary for transactivation. Surprisingly, analogous studies in wild-type and DBP-null mice, wherein we explored the activity of exogenous 1,25(OH)(2)D(3), produced strikingly different results as compared with those in vitro. Here, the carrier protein had virtually no impact on the distribution, uptake, activation profile, or biological potency of the hormone. Collectively, these experiments suggest that whereas DBP is important to total circulating 1,25(OH)(2)D(3) and sequesters extracellular levels of this hormone both in vivo and in vitro, the binding protein does not influence the hormone's biologically active pool.

Gc-globulin: roles in response to injury

BACKGROUND

Gc-globulin (vitamin D-binding protein) appears to have important functions in addition to its role as a carrier of vitamin D.

APPROACH

We reviewed recent studies focusing on the pathophysiologic functions and clinical significance of Gc-globulin.

RESULTS

Serum concentrations of Gc-globulin, as determined by immunoassay techniques, are decreased in severe injury. The extent of the decrease may have prognostic significance for patient outcomes. Clinical studies and animal models have shown that Gc-globulin has an important role in the clearance of procoagulant actin from the circulation after its release during cell necrosis and tissue injury. Gc-globulin has other potential roles in responses to acute tissue injury through conversion to a macrophage-activating factor, neutrophil chemotactic activity, and enhancement of C5a-mediated signaling.

CONCLUSION

Considering the important physiologic roles of Gc-globulin in responses to tissue injury, such as clearance of actin, measurement of Gc-globulin may have value in directing the care of patients in many clinical disorders.

Biological and clinical aspects of the vitamin D binding protein (Gc-globulin) and its polymorphism

The vitamin D binding protein (DBP) is the major plasma carrier protein of vitamin D and its metabolites. Unlike other hydrophobic hormone-binding systems, it circulates in a considerably higher titer compared to its ligands. Apart from its specific sterol binding capacity, DBP exerts several other important biological functions such as actin scavenging, fatty acid transport, macrophage activation and chemotaxis. The DBP-gene is a member of a multigene cluster that includes albumin, alpha-fetoprotein, and alpha-albumin/afamin. All four genes are expressed predominantly in the liver with overlapping developmental profiles. DBP is a highly polymorphic serum protein with three common alleles (Gc1F, Gc1S and Gc2) and more than 120 rare variants. The presence of unique alleles is a useful tool for anthropological studies to discriminate and to reveal ancestral links between populations. Many studies have discussed the link between DBP-phenotypes and susceptibility or resistance to osteoporosis, Graves' disease, Hashimoto's thyroiditis, diabetes, COPD, AIDS, multiple sclerosis, sarcoidosis and rheumatic fever. This article reviews the general characteristics, functions and clinical aspects of DBP.

Inhibition of angiogenesis by vitamin D-binding protein: characterization of anti-endothelial activity of DBP-maf

Angiogenesis is a complex process involving coordinated steps of endothelial cell activation, proliferation, migration, tube formation and capillary sprouting with participation of intracellular signaling pathways. Regulation of angiogenesis carries tremendous potential for cancer therapy. Our earlier studies showed that vitamin D-binding protein-macrophage activating factor (DBP-maf) acts as a potent anti-angiogenic factor and inhibits tumor growth in vivo. The goal of this investigation was to understand the effect of DBP-maf on human endothelial cell (HEC) and the mechanism of angiogenesis inhibition. DBP-maf inhibited human endothelial cell (HEC) proliferation by inhibiting DNA synthesis (IC(50) = 7.8 +/- 0.15 microg/ml). DBP-maf significantly induced S- and G0/G1-phase arrest in HEC in 72 h. DBP-maf potently blocked VEGF-induced migration, tube-formation of HEC in a dose dependent manner. In addition, DBP-maf inhibited growth factor-induced microvessel sprouting in rat aortic ring assay. Moreover, DBP-maf inhibited VEGF signaling by decreasing VEGF-mediated phosphorylation of VEGFR-2 and ERK1/2, a downstream target of VEGF signaling cascade. However, Akt activation was not affected. These studies collectively demonstrate that DBP-maf inhibits angiogenesis by blocking critical steps such as HEC proliferation, migration, tube formation and microvessel sprouting. DBP-maf exerts its effect by inhibiting VEGR-2 and ERK1/2 signaling cascades. Understanding the cellular and molecular mechanisms of anti-endothelial activity of DBP-maf will allow us to develop it as an angiogenesis targeting novel drug for tumor therapy.

Gc protein (vitamin D-binding protein): Gc genotyping and GcMAF precursor activity

The Gc protein (human group-specific component (Gc), a vitamin D-binding protein or Gc globulin), has important physiological functions that include involvement in vitamin D transport and storage, scavenging of extracellular G-actin, enhancement of the chemotactic activity of C5a for neutrophils in inflammation and macrophage activation (mediated by a GalNAc-modified Gc protein (GcMAF)). In this review, the structure and function of the Gc protein is focused on especially with regard to Gc genotyping and GcMAF precursor activity. A discussion of the research strategy "GcMAF as a target for drug discovery" is included, based on our own research.

Identification of a Region in the Vitamin D-binding Protein that Mediates Its C5a Chemotactic Cofactor Function

The vitamin D-binding protein (DBP), also known as group-specific component or Gc-globulin, is a multifunctional plasma protein that can significantly enhance the leukocyte chemotactic activity to C5a and C5a des-Arg. DBP is a member of the albumin gene family and has a triple domain modular structure with extensive disulfide bonding that is characteristic of this protein family. The goal of this study was to identify a region in DBP that mediates the chemotactic cofactor function for C5a. Full-length and truncated versions of DBP (Gc-2 allele) were expressed in Escherichia coli using a glutathione S-transferase fusion protein expression system. The structure of the expressed proteins was confirmed by SDS-PAGE and immunoblotting, whereas protein function was verified by quantitating the binding of [(3)H]vitamin D. Dibutyryl cAMP-differentiated HL-60 cells were utilized to test purified natural DBP and recombinant expressed DBP (reDBP) for their ability to enhance chemotaxis and intracellular Ca(2+) flux to C5a. Natural and full-length reDBP (458 amino acid residues) as well as truncated reDBPs that contained the N-terminal domain I (domains I and II, residues 1-378; domain I, residues 1-191) significantly enhanced both cell movement and intracellular Ca(2+) concentrations in response to C5a. Progressive truncation of DBP domain I localized the chemotactic enhancing region between residues 126-175. Overlapping peptides corresponding to this region were synthesized, and results indicate that a 20-amino-acid sequence (residues 130-149, 5'-EAFRKDPKEYANQFMWEYST-3') in domain I of DBP is essential for its C5a chemotactic cofactor function.

Platelet-derived thrombospondin-1 is necessary for the vitamin D-binding protein (Gc-globulin) to function as a chemotactic cofactor for C5a

The chemotactic activity of C5a and C5a des Arg can be enhanced significantly by the vitamin D-binding protein (DBP), also known as Gc-globulin. DBP is a multifunctional 56-kDa plasma protein that binds and transports several diverse ligands. The objective of this study was to investigate the mechanisms by which DBP functions as a chemotactic cofactor for C5a using neutrophils and U937 cells transfected with the C5aR (U937-C5aR cells). The results demonstrate that U937-C5aR cells show C5a chemotactic enhancement only to DBP in serum, but, unlike mature neutrophils, this cell line cannot respond to DBP in plasma or to purified DBP. Analysis by SDS-PAGE and isoelectric focusing revealed no structural difference between DBP in serum compared with DBP in plasma. However, plasma supplemented with either serum, DBP-depleted serum, or activated platelet releasate provides a required factor and permits DBP to function as a chemotactic cofactor for C5a. Fractionation of activated platelet releasate revealed that the additional factor possessed the properties of thrombospondin-1 (TSP-1). Finally, purified TSP-1 alone could reproduce the effect of serum or platelet releasate, whereas Abs to TSP-1 could block these effects. These results provide clear evidence that TSP-1 is needed for DBP to function as a chemotactic cofactor for C5a.

Simultaneous detection of ACP1 and GC genotypes using PCR/SSCP

The classical enzyme and protein markers ACP1 and GC have gained new importance because of the biological functions of their gene products. ACP1 encodes a low molecular weight enzyme which is now recognized as a phosphotyrosine phosphatase with a role in the regulation of signal transduction pathways, and GC-globulin acts both as a transporter of vitamin D and as a plasma actin scavenger and plays a role in macrophage activation. These two polymorphisms were phenotyped for decades on the basis of electrophoretic isozyme or protein patterns; the gene structures are now known. Nucleotide substitutions determining the common alleles are close enough at each locus to be contained in one short PCR product. We have developed a simple, rapid and reliable multiplex method based on PCR and SSCP which allows the simultaneous determination of the common ACP1 and GC genotypes.

Therapeutic uses of vitamin D analogues

The vitamin D endocrine system has been implicated in numerous biological activities throughout the body. The breadth and magnitude of vitamin D activity suggest potential therapeutic applications for the treatment of several diseases and disorders, including hyperproliferative diseases, immune dysfunction, endocrine disorders, and metabolic bone diseases. However, therapy using natural vitamin D hormone, 1,25-dihydroxyvitamin D(3) (1,25[OH](2)D(3)) has been precluded in most cases because of the potent calcemic activity shown by this hormone. Newly developed vitamin D analogues with lower calcemic activity have been shown to retain many therapeutic properties of 1,25(OH)(2)D(3). Molecular studies discussed in this article provide insights into the unique target cell specificity afforded by these analogues. In particular, the importance of the nuclear vitamin D receptor (VDR), serum vitamin D-binding protein, 24-hydroxylase, and membrane receptor is noted because analogue selectivity, specificity, and potency are afforded through their molecular interactions. The nuclear VDR has been isolated from a variety of target cells and tissues, suggesting that vitamin D compounds may have therapeutic potential throughout several body systems. Five vitamin D analogues have been approved for use in patients: calcipotriol (Dovonex; Leo Pharmaceuticals, Copenhagen, Denmark) for the treatment of psoriasis, 19-nor-1,25(OH)(2)D(2) (Zemplar; Abbott Laboratories, Abbott Park, IL) for secondary hyperparathyroidism, doxercalciferol (Hectorol; Bone Care Int, Madison, WI) for reduction of elevated parathyroid hormone levels, 22-oxacalcitriol (Maxacalcitol; Chugai Pharmaceuticals, Tokyo, Japan), and alfacalcidol. Several other analogues are currently being tested in preclinical and clinical trials for the treatment of various types of cancer and osteoporosis, as well as immunosuppression. Understanding how analogues exert their selective actions may allow for the design of more effective and safer vitamin D compounds for the treatment of a wide range of clinical disorders.

Baculovirus-expressed vitamin D-binding protein-macrophage activating factor (DBP-maf) activates osteoclasts and binding of 25-hydroxyvitamin D(3) does not influence this activity

Vitamin D-binding protein (DBP) is a multi-functional serum protein that is converted to vitamin D-binding protein-macrophage activating factor (DBP-maf) by post-translational modification. DBP-maf is a new cytokine that mediates bone resorption by activating osteoclasts, which are responsible for resorption of bone. Defective osteoclast activation leads to disorders like osteopetrosis, characterized by excessive accumulation of bone mass. Previous studies demonstrated that two nonallelic mutations in the rat with osteopetrosis have independent defects in the cascade involved in the conversion of DBP to DBP-maf. The skeletal defects associated with osteopetrosis are corrected in these mutants with in vivo DBP-maf treatment. This study evaluates the effects of various forms of DBP-maf (native, recombinant, and 25-hydroxyvitamin D(3) bound) on osteoclast function in vitro in order to determine some of the structural requirements of this protein that relate to bone resorbing activities. Osteoclast activity was determined by evaluating pit formation using osteoclasts, isolated from the long bones of newborn rats, incubated on calcium phosphate coated, thin film, Ostologic MultiTest Slides. Incubation of osteoclasts with ex vivo generated native DBP-maf resulted in a dose dependent, statistically significant, activation of the osteoclasts. The activation was similar whether or not the vitamin D binding site of the DBP-maf was occupied. The level of activity in response to DBP-maf was greater than that elicited by optimal doses of other known stimulators (PTH and 1,25(OH(2)D(3)) of osteoclast function. Furthermore, another potent macrophage activating factor, interferon--gamma, had no effect on osteoclast activity. The activated form of a full length recombinant DBP, expressed in E. coli showed no activity in the in vitro assay. Contrary to this finding, baculovirus-expressed recombinant DBP-maf demonstrated significant osteoclast activating activity. The normal conversion of DBP to DBP-maf requires the selective removal of galactose and sialic acid from the third domain of the protein. Hence, the differential effects of the two recombinant forms of DBP-maf is most likely related to glycosylation; E. coli expressed recombinant DBP is non-glycosylated, whereas the baculovirus expressed form is glycosylated. These data support the essential role of glycosylation for the osteoclast activating property of DBP-maf.

Cloning, sequencing, and functional characterization of the vitamin D receptor in vitamin D-resistant New World primates

New World primates (NWPs) have high circulating 1,25-dihydroxyvitamin D (1,25-(OH)2D) levels. Comparable levels would be harmful to Old World primates (OWPs) and humans. Thus, NWPs must have developed mechanisms of 1,25-(OH)2D resistance to survive. In humans, patients with hypocalcemic vitamin D-resistant rickets type II have high circulating vitamin D levels and vitamin D resistance due to expression of a dysfunctional vitamin D receptor (VDR). To examine if this could wholly or in part explain vitamin D resistance in NWPs, VDR from Saguinus oedipus (cotton top tamarin) NWP B95-8 cells was cloned by reverse-transcription polymerase chain reaction (RT-PCR). The NWP VDR cDNA sequence showed 96% homology at the DNA level and 98% homology at the amino acid level compared to human VDR. To assay for function, NWP VDR cDNA was transiently transfected into CV-1 cells with a vitamin D response element reporter plasmid. No difference between OWP and NWP VDR-directed transactivation was observed. These results indicate that the mechanism of vitamin D resistance in NWPs is not due to a dysfunctional VDR, and is consistent with our hypothesis that vitamin D resistance in NWPs is mediated by overexpression of a VDR-independent vitamin D response element binding protein.

Elastase controls the binding of the vitamin D-binding protein (Gc-globulin) to neutrophils: a potential role in the regulation of C5a co-chemotactic activity

The vitamin D-binding protein (DBP) binds to the plasma membranes of numerous cell types and mediates a diverse array of cellular functions. DBP bound to the surface of leukocytes serves as a co-chemotactic factor for C5a, significantly enhancing the chemotactic activity of pM concentrations of C5a. This study investigated the regulation of DBP binding to neutrophils as a possible key step in the process of chemotaxis enhancement to C5a. Using radioiodinated DBP as a probe, neutrophils released 70% of previously bound DBP into the extracellular media during a 60-min incubation at 37 degrees C. This was suppressed by serine protease inhibitors (PMSF, Pefabloc SC), but not by metallo- or thiol-protease inhibitors. DBP shed from neutrophils had no detectable alteration in its m.w., suggesting that a serine protease probably cleaves the DBP binding site, releasing DBP in an unaltered form. Cells treated with PMSF accumulate DBP vs time with over 90% of the protein localized to the plasma membrane. Purified neutrophil plasma membranes were used to screen a panel of protease inhibitors for their ability to suppress shedding of the DBP binding site. Only inhibitors to neutrophil elastase prevented the loss of membrane DBP-binding capacity. Moreover, treatment of intact neutrophils with elastase inhibitors prevented the generation of C5a co-chemotactic activity from DBP. These results indicate that steady state binding of DBP is essential for co-chemotactic activity, and further suggest that neutrophil elastase may play a critical role in the C5a co-chemotactic mechanism.

The vitamin D response element-binding protein. A novel dominant-negative regulator of vitamin D-directed transactivation

Vitamin D resistance in certain primate genera is associated with the constitutive overexpression of a non-vitamin D receptor (VDR)-related, vitamin D response element-binding protein (VDRE-BP) and squelching of vitamin d-directed transactivation. We used DNA affinity chromatography to purify proteins associated with non-VDR-VDRE binding activity from vitamin d-resistant New World primate cells. In electrophoretic mobility shift assays, these proteins bound specifically to either single-strand or double-strand oligonucleotides harboring the VDRE. Amino acid sequencing of tryptic peptides from a 34-kDa (VDRE-BP1) and 38-kDa species (VDRE-BP-2) possessed sequence homology with human heterogeneous nuclear ribonucleoprotein (hnRNP) A1 and hnRNPA2, respectively. cDNAs bearing the open reading frame for both VDRE-BPs were cloned and used to transfect wild-type, hormone-responsive primate cells. Transient and stable overexpression of the VDRE-BP2 cDNA, but not the VDRE-BP1 cDNA, in wild-type cells with a VDRE-luciferase reporter resulted in significant reduction in reporter activity. These data suggest that the hnRNPA2-related VDRE-BP2 is a dominant-negative regulator of vitamin D action.

The toothless osteopetrotic rat has a normal vitamin D-binding protein-macrophage activating factor (DBP-MAF) cascade and chondrodysplasia resistant to treatments with colony stimulating factor-1 (CSF-1) and/or DBP-MAF

The osteopetrotic rat mutation toothless (tl) is characterized by little or no bone resorption, few osteoclasts and macrophages, and chondrodysplasia at the growth plates. Short-term treatment of tl rats with colony-stimulating factor-1 (CSF-1) has been shown to increase the number of osteoclasts and macrophages, producing dramatic resolution of skeletal sclerosis at some, but not all, sites. Defects in production of vitamin D-binding protein-macrophage activating factor (DBP-MAF) have been identified in two other independent osteopetrotic mutations of the rat (op and ia), and two in the mouse (op and mi), in which macrophages and osteoclasts can be activated by the administration of exogenous DBP-MAF. The present studies were undertaken to examine the histology and residual growth defects in tl rats following longer CSF-1 treatments, to investigate the possibility that exogenous DBP-MAF might act synergistically with CSF-1 to improve the tl phenotype, and to assess the integrity of the endogenous DBP-MAF pathway in this mutation. CSF-1 treatment-with or without DBP-MAF-induced resorption of metaphyseal bone to the growth plate on the marrow side, improved slightly but did not normalize long bone growth, and caused no improvement in the abnormal histology of the growth plate. Injections of lysophosphatidylcholine (lyso-Pc) to prime macrophage activation via the DBP-MAF pathway raised superoxide production to similar levels in peritoneal macrophages from both normal and mutant animals, indicating no defect in the DBP-MAF pathway in tl rats. Interestingly, pretreatments with CSF-1 alone also increased superoxide production, although the mechanism for this remains unknown. In summary, we find that, unlike other osteopetrotic mutations investigated to date, the DBP-MAF pathway does not appear to be defective in the tl rat; that additional DBP-MAF does not augment the beneficial skeletal effects seen with CSF-1 alone; and that the growth plate chondrodystrophy seen in this mutation is unaffected by either molecule. Thus, the tl mutation intercepts the function of a gene required for both normal endochondral ossification and bone resorption, thereby uncoupling the coordination of skeletal metabolism required for normal long bone growth.

Vitamin D binding protein variants and the risk of COPD

Although the development of chronic obstructive pulmonary disease (COPD) in smokers shows genetic susceptibility, only alpha1-antitrypsin deficiency has been identified as a definite genetic risk factor. There have been three previous studies in which associations between Gc-globulin phenotypes and COPD have been investigated. Although some data suggest an association, the results were inconclusive. Because smoking is the major risk factor for COPD, it may have been a confounding factor in previous studies. We have investigated Gc-globulin genotypic frequencies among 75 COPD patients and 64 nonobstructed controls. Both groups had significant smoking histories: pack-years (mean +/- SD) of 52 +/- 30 and 48 +/- 27, respectively. The results show that homozygosity for the Gc2 allele is protective against COPD (OR = 0.17, 95% CI = 0.03 to 0.83). There were no differences between genotypes for lung elastic recoil values or for the level of upstream airway resistance. Gc-globulin can enhance complement (C5a)-mediated neutrophil chemotaxis. Because neutrophils play a role in parenchymal destruction and airway inflammation, we examined whether Gc-globulin's ability to enhance neutrophil chemotaxis varied with genotype. We found no difference among genotypes with respect to neutrophil chemotaxis suggesting that the protective effect of the Gc2 allele is mediated through a different mechanism.

Role of vitamin D3-binding protein in activation of mouse macrophages

When mouse peritoneal nonadherent (lymphocytes) cells were treated with lysophosphatidylcholine (lyso-Pc) and cultured with adherent cells (macrophages) in 1% fetal calf serum (FCS)- or adult mouse serum (AMS)-supplemented medium for 3 h, markedly enhanced phagocytic and superoxide-generating capacities of macrophages were observed. Stepwise cultivation of lyso-Pc-treated B cells and untreated T cells with an FCS-supplemented medium generated a macrophage-activating factor (MAF), whereas cultivation of lyso-Pc-treated B cells alone in AMS-supplemented medium was sufficient to generate the MAF. The accumulated evidence suggests that lyso-Pc-inducible beta-galactosidase of B lymphocytes and the Neu-1 sialidase of T lymphocytes modified the bovine serum vitamin D3-binding protein (DBP) to yield the MAF, a protein with N-acetylgalactosamine as the remaining sugar. In contrast, the lyso-Pc-inducible beta-galactosidase of B cells alone modified mouse DBP to yield the MAF. These observations led us to conclude that bovine DBP carries a trisaccharide composed of N-acetylgalactosamine, galactose, and sialic acid, whereas mouse DBP carries a disaccharide composed of N-acetylgalactosamine and galactose. Thus, macrophages of a T-cell-deficient nude (BALB/c nu/nu) mouse and a T-cell Neu-1 sialidase-deficient SM/J mouse were efficiently activated by administration of lyso-Pc.

Animal models of osteopetrosis: the impact of recent molecular developments on novel strategies for therapeutic intervention

Osteopetrosis comprises a group of rare metabolic diseases of skeletal development that are characterized by a generalized increase in skeletal mass resulting from reduced osteoclast-mediated bone resorption. Specific immune regulators and growth factors that influence osteoclast ontogeny and/or activation have been implicated in the pathogenesis of some of the naturally occurring mutations associated with osteopetrosis in animals. Most recently, loss-of-function experiments using transgenic mice with targeted disruptions of the c-src or c-fos proto-oncogenes have resulted in different osteoclast abnormalities that produce osteopetrosis. The information gained from these mutations in animals should continue to provide new understanding of the molecular defects associated with osteopetrosis, and to broader aspects of skeletal pathology; this should result in more effective therapeutic intervention in humans.

Tandem arrangement of the human serum albumin multigene family in the sub-centromeric region of 4q: evolution and chromosomal direction of transcription

The albumin gene family is comprised of four genes encoding: serum albumin (ALB), alpha-fetoprotein (AFP), alpha-albumin (ALF), and vitamin D-binding protein (DBP; also known as GC). The genes are regulated developmentally, expressed in the liver, and the proteins are secreted into the bloodstream. The GC gene, and the tandemly linked ALB and AFP genes, have been previously localized to human chromosome 4q11-13. Using techniques of fluorescence in situ hybridization to chromatin fibres, chromosome walking and DNA sequencing of genomic clones, we now report on the chromosomal location of the ALF gene and the organization of the entire gene family. The four genes are tandemly linked in the 4q sub-centromeric region: 5'ALB-5'AFP-5'ALF-5'GC3'-centromere, and hence are transcribed in the same, centromere-bound, direction. The linear arrangement of the four genes along the chromosome is not correlated with their temporal expression in the human ontogeny. It appears that GC is very close (and may be the gene proximal) to the centromere. The linear chromosomal arrangement of the four genes and the structural differences between them are congruent with the following evolutionary divergence of the gene family. Starting with the first duplication of an ancestral progenitor gene, a single evolutionary line led to the contemporary GC, leaving ALB/AFP/ALF on the other line of descent. The second duplication occurred in this ALB lineage, giving rise to ALB and the AFP/ALF progenitor, and the third, most recent one, gave rise to the AFP-ALF pair.

Plasma vitamin D-binding protein (Gc-globulin): multiple tasks

The transporter of vitamin D and its metabolites in blood has received increasing attention in recent years, and is recognized to be a member of a gene family that includes albumin and alpha-fetoprotein. Identical to the group specific component (Gc-globulin) of serum, the protein is a single-chain polypeptide constitutively synthesized in liver that circulates in amounts in far excess of normal vitamin D metabolite concentrations in blood. It plays the major role in the egress of endogenously synthesized vitamin D, from skin and appears to restrain D-sterols from too rapid/excessive cell entry. Along with plasma gelsolin, it comprises the plasma actin-scavenger system that facilitates removal of actin, liberated from lysed cells, by depolymerization and prevention of polymerization. Recently, the protein has been shown to behave as a co-chemotaxin specific for the complement peptide C5a, and its sialic acid-free form has been reported to play a role in macrophage activation. The latter functions strongly implicate its participation in inflammation responses. A unifying hypothesis might also suggest the protein to provide focal D-sterol delivery to cells that are important to the resolution of tissue injuries.

Human testis vitamin D binding protein involved in infertility

Immunoglobulin G (IgG) fraction was prepared from a serum obtained from an infertile woman containing antisperm antibodies that induced head-to-head agglutination of human sperm. The antibodies in the IgG fraction interacted with a 60-kD protein found in human testes determined by Western blot. The 60-kD protein was purified from human testis by isoelectric focusing (IEF), affinity chromatography on blue sepharose column, and preparative electrophoresis with electroelution. The purified 60-kD protein migrated as a single homogeneous band when analyzed by SDS-PAGE. The amino acid sequence of the N-terminus was determined. The initial 10 amino acid residues were identical to the human serum vitamin D binding protein (VDBP). Polyclonal antibodies were raised against the 60-kD protein. The polyclonal anti-60-kD antibodies and the anti-VDBP antibodies obtained from a commercial source immobilized human sperm in vitro. The interacting antigens were located on the postacrosomal region and midpiece of human sperm, as determined by an immunofluorescence method. The IgG fraction prepared from the serum of an infertile woman interacted with the human testis 60-kD protein but failed to stain serum VDBP. The results suggest that the 60-kD and VDBP are related proteins but not identical entities and that the 60-kD protein contains a unique structural group lacking in serum VDBP. Production of antibodies against the unique structure of the 60-kD protein may be the cause of the infertility.

Human prostate cancer cells: inhibition of proliferation by vitamin D analogs

1,25-Dihydroxyvitamin D [1,25(OH)2D3, calcitriol] can inhibit the proliferation of some human prostate cancer cells but its clinical use is limited by hypercalcemia. We therefore explored the bioactivity of less calcemic vitamin D analogs. We studied the effects of calcitriol and 3 synthetic analogs at concentrations of 10(-6) to 10(-12) M on the in vitro proliferation of 3 human prostate carcinoma cell lines: DU 145, PC-3, and LNCaP. Calcitriol and analogs showed significant antiproliferative activity on PC-3 and LNCaP cells. DU 145 cells were inhibited by the analogs only. We conclude that vitamin D analogs warrant further investigation as therapeutic agents in prostate cancer.

A single up-stream element confers responsiveness to 1,25-dihydroxyvitamin D3 and tumor necrosis factor-alpha in the rat osteocalcin gene

Tumor necrosis factor-alpha (TNF alpha) is one of several autocrine/paracrine factors known to exert potent inhibitory effects on bone. We have shown that TNF alpha inhibition of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]-stimulated synthesis of the bone-specific protein osteocalcin (OC) occurs by decreasing steady state levels of OC mRNA, suggesting a pretranslational mechanism. In many genes, TNF alpha action is mediated by the transcription factor NF kappa B. Analysis of OC 5'-flanking DNA revealed a sequence structurally homologous to the previously described NF kappa B-binding site and, thus, a potential TNF alpha response element. Deletion analysis was performed to identify the sequences mediating the response to TNF alpha in osteoblastic ROS 17/2.8 cells by transient transfection with reporter constructs containing rat OC 5'-flanking DNA [chloramphenicol acetyltransferase (CAT)] that retained or deleted homologous NF kappa B sites or a previously defined 1,25-(OH)2D3 response element (VDRE). Transfection with all reporter constructs resulted in low basal CAT activity, measured 72 h after transfection. 1,25-(OH)2D3 stimulated CAT activity 2.8- to 4.5-fold in cells transfected with constructs that included the VDRE. TNF alpha inhibited 1,25-(OH)2D3-stimulated, but not basal, CAT activity. Deletion analysis localized the effect of TNF alpha to a sequence between -522 and -306 relative to the OC transcription start site, an area that included the VDRE but deleted a homologous NF kappa B element. Transfection of cells with a heterologous reporter containing one copy of the OC VDRE inserted in correct orientation or two copies in inverse orientation was sufficient to confer a response to TNF alpha. Gel mobility shift analysis of DNA-nuclear protein interaction revealed that 1,25-(OH)2D3 stimulated an increase in binding of nuclear proteins to an OC 32P-VDRE probe. Preincubation of nuclear extract with specific monoclonal antibodies confirmed that the proteins binding the VDRE included the vitamin D receptor and retinoid-X receptor. TNF alpha treatment of cells inhibited the 1,25-(OH)2D3-stimulated increase in nuclear protein binding to the VDRE. These results suggest 1) the VDRE is sufficient to confer a response to the inhibitory effect of TNF alpha on 1,25-(OH)2D3-stimulated rat OC gene transcription; 2) the action of TNF alpha does not require homologous NF kappa B response elements; and 3) the mechanism of TNF alpha inhibition of 1,25-(OH)2D3-stimulated OC gene expression includes modulation of binding of the vitamin D receptor/retinoid-X receptor heterodimer to the VDRE.

Human monocyte chemotaxis to complement-derived chemotaxins is enhanced by Gc-globulin

Gc-globulin has been found in bronchoalveolar lavage fluid in patients with chronic obstructive pulmonary disease (COPD) and adult respiratory distress syndrome (ARDS) and has been shown to enhance neutrophil chemotaxis to C5-derived peptides in vitro. We proposed that Gc-globulin may enhance the inflammatory response in lungs by influencing monocyte chemotaxis to C5-derived peptides as it does with neutrophils. Monocyte chemotaxis was measured in blind well chambers by a leading-front technique. Purified human Gc-globulin had no intrinsic chemotactic activity for monocytes at concentrations ranging from 1 fM to 1 microM. However, Gc-globulin, at concentrations as low as 10 pM, increased monocyte chemotaxis over 10-fold in a concentration-dependent fashion when added to non-chemotactic doses of C5a (0.1 nM) and C5a des Arg (0.5 nM). The chemotaxis-enhancing effect of Gc-globulin was specific for C5-derived peptides, as Gc-globulin did not enhance monocyte chemotaxis to other chemoattractants such as leukotriene B4 or formyl-Met-Leu-Phe. The enhancement of monocyte chemotaxis to C5-derived peptides by Gc-globulin was not a nonspecific effect of anionic proteins, as other serum proteins of similar size and charge did not enhance monocyte chemotaxis to C5a des Arg. These results indicate that Gc-globulin enhances the monocyte response to C5-derived peptides and, together with previous work, indicates that its presence in the airways of patients with COPD and ARDS may up-regulate the monocyte inflammatory response in the lungs.

Thyroxine-binding protein represents the major vitamin D-binding protein in the plasma of the turtle, Trachemys scripta

Structural homology between the high-affinity thyroxine (T4)-binding protein (TBP) in the plasma of the turtle, Trachemys scripta, and vitamin D-binding proteins (DBP) of mammals prompted an investigation of plasma vitamin D binding in the turtle. Several lines of evidence indicate that the TBP represents the primary binding protein for 25-OH-cholecalciferol (D3) in the turtle plasma. D3-binding protein in whole plasma migrates in the same position as TBP by size-exclusion chromatography and polyacrylamide gel electrophoresis; it is electrophoretically distinct from sex hormone-binding proteins. D3 binding to purified TBP alone is enhanced (up to sevenfold) in the presence of plasma proteins, including albumin; with this correction, the D3-binding activity of plasma corresponds to expected TBP titers. Plasma selectively stripped of TBP by affinity chromatography and purified turtle albumin have only trace D3-binding activity. Variations in physiological state (thyroidal status, age, and sex) previously associated with variable T4 binding (and TBP levels) in T. scripta show correlated variability in plasma D3 binding. D3 binding is also highly correlated with T4 binding (r = 0.81; P < 0.001) for plasma samples taken from 30 adults representing 10 different species of Trachemys. D3 binding in plasma exhibits a high-affinity site (Ka = 2.3 x 10(8) M-1) and a second lower-affinity (Ka = 2 x 10(6) M-1), higher-capacity site; capacities are highly variable. Purified TBP has a comparable high affinity (Ka = 2.8 x 10(8) M-1), with a capacity close to 1 mol/mol. Binding of T4 and D3 are not competitive, indicating separate binding sites for the two ligands; in fact, T4 tends to enhance the affinity and the capacity for D3. A single protein in turtle plasma ("TBP/DBP") functions in the transport of two different hormones normally served by two distinct binding proteins (representing different multigene families) in mammals. These results have implications for the mediation of T4 effects on growth.

Identification of the serum factor required for in vitro activation of macrophages. Role of vitamin D3-binding protein (group specific component, Gc) in lysophospholipid activation of mouse peritoneal macrophages

In vitro treatment of mouse peritoneal cells (mixture of adherent and nonadherent cells) with lysophosphatidylcholine (lyso-Pc) in 10% FCS supplemented medium RPMI 1640 results in a greatly enhanced FcR-mediated phagocytic activity of macrophages. This macrophage-activation process requires a serum factor. Fractionation studies with starch block electrophoresis of fetal calf and human sera revealed that alpha 2-globulin fraction contains a serum factor essential for macrophage activation. To identify the serum factor, human serum was precipitated with 50% saturated ammonium sulfate and fractionated on a Sephadex G-100 column. A protein fraction with a lower m.w. than albumin had the capacity to support activation of macrophages. The active serum factor in this protein fraction was analyzed by immunoabsorption by using rabbit antisera against three major proteins of human alpha 2-globulin. This active serum factor was shown to be a vitamin D3-binding protein (group specific component, Gc). By using a monoclonal anti-Gc-absorbed active column fraction of human serum, we observed no enhanced macrophage activation over the results with serum fraction-free cultivation of lyso-Pc-treated peritoneal cells. Cultivation of lyso-Pc-treated peritoneal cells in a medium containing a low concentration of purified human Gc protein (0.1 to 2.6 ng/ml) produced a greatly enhanced phagocytic activity of macrophages. When purified human Gc protein was used in a serum-free medium for stepwise cultivation of lyso-Pc-treated nonadherent cell types, a macrophage-activating factor was efficiently generated. Therefore, it is concluded that the vitamin D3-binding protein is the essential serum factor for the lyso-Pc-primed activation of macrophages.

1,25-Dihydroxycholecalciferol inhibits the cochemotactic activity of Gc (vitamin D binding protein)

The identification of Gc (vitamin D binding protein) with the anionic polypeptide cochemotaxin has recently been reported. In this paper we investigate its dose dependent cochemotactic activity and report the inhibition of Gc enhanced chemotaxis by vitamin D3. These results further support the role of immunomodulating hormone played by vitamin D.

Gcglobulin functions as a cochemotaxin in the lower respiratory tract. A potential mechanism for lung neutrophil recruitment in cigarette smokers

Activation of the complement pathway with generation of the potent chemotaxin C5a may play a significant role in the neutrophil accumulation seen in the lungs of patients with smoking-associated diseases. Although C5a is rapidly degraded to the less potent chemotaxin C5a des Arg, binding of this peptide with its cochemotaxin Gcglobulin (GcG) can restore its chemotactic potency. Therefore, modulation of Gcglobulin levels in smoking-induced lung disease could affect the accumulation of neutrophils seen in this disorder. To test this hypothesis GcG was measured by an enzyme-linked immunosorbent assay in bronchoalveolar lavage fluids (BALF) obtained from non-smokers, asymptomatic smokers, and patients with chronic obstructive pulmonary disease (COPD). Antigenic amounts of GcG in BALF were increased in COPD patients and asymptomatic smokers compared with nonsmokers (6.35 +/- 1.02 and 5.15 +/- 1.07 versus 2.82 +/- 0.37 micrograms/mg albumin, p less than 0.05). In addition, we found that BALF enhanced C5a des Arg-mediated chemotaxis (48.3 +/- 5.6 versus 11.2 +/- 1.6 cells/high power field, p less than 0.05), an effect that was not seen in the presence of GcG antibody. Furthermore, BALF GcG was similar to serum GcG using Western blot analysis, and the interaction of GcG with C5a des Arg was not inhibited by cigarette smoke. These data demonstrate that elevation of BALF GcG levels occurs in smoking-associated lung disease and that this protein is biologically active and capable of increasing C5a des Arg-mediated chemotaxis. This suggests that modulation of GcG levels may be important in smoking-associated lung diseases.

Albuminoid molecules: a novel, variability-generating cell-surface receptor system?

The mechanisms by which lymphoid cells produce infinitely variable molecules of the immunoglobulin protein superfamily have been recently elucidated. These molecules serve, in part, as the mediators of cell:cell recognition and interaction among lymphoid cells. However, the generality of those molecular mechanisms to occur in non-lymphoid cell types has not yet been established. In this paper, we propose that the serum albumin superfamily of proteins has the necessary characteristics to serve analogous functions in epithelioid cells, and we critique recent evidence which leads to this hypothesis.

25 Hydroxyvitamin D and vitamin E absorption in healthy children and children with chronic intrahepatic cholestasis

Patients with chronic cholestasis have reduced 25-hydroxyvitamin D (25OHD) and vitamin E levels. We determined serum concentrations of 25OHD, 1,25-dihydroxyvitamin D [1,25(OH)2D] and vitamin E before and after oral administration of 10 micrograms/kg body weight 25-hydroxyvitamin D3 (25OHD3) and 100 IU/kg body weight vitamin E, respectively, in 4 patients with intrahepatic cholestasis and 6 healthy children. Vitamin E increased in all controls but in only one of the four patients. In contrast, oral 25OHD3 induced a normal rise in circulating 25OHD and 1,25(OH)2D. The low serum levels of 25OHD in the patients before the oral bolus may have been due to inadequate parenteral vitamin D administration and/or to the simultaneous phenobarbital treatment. The latter possibility is supported by the increase of serum 25OHD into the normal range after withdrawal of phenobarbital in one of the four patients. We conclude that vitamin E has to be supplemented parenterally or in water-soluble oral form. Further studies are necessary to clarify whether high-dose long-term oral 25OHD3 supplementation is sufficient to prevent vitamin D deficiency in patients with chronic cholestasis.

Gc-globulin (vitamin D-binding protein) enhances the neutrophil chemotactic activity of C5a and C5a des Arg

Several serum proteins have been shown to be important in modulating leukocyte chemotaxis and inflammation. We investigated the possibility that the multifunctional serum protein Gc-globulin (vitamin D-binding protein) may also enhance the neutrophil chemotactic activity of complement-derived peptides. Purified Gc-globulin by itself did not induce chemotaxis of human neutrophils. However, as little as 0.01 nM Gc-globulin greatly enhanced the neutrophil chemotactic activity of C5a and its derivative, C5a des Arg over a wide concentration range. The effect was most pronounced at nonchemotactic doses of C5a (0.01 nM) and C5a des Arg (1 nM). Gc-globulin was unable to augment the neutrophil chemotactic activity of FMLP and leukotriene B4. This enhancing activity was not due to a nonspecific effect of anionic proteins since other purified serum proteins, of similar size and charge as Gc-globulin (alpha 1 acid glycoprotein, alpha 2 HS glycoprotein, alpha 2 histidine-rich glycoprotein), could not increase the chemotactic activity of C5a des Arg. Serum depleted of Gc-globulin by immunoaffinity chromatography totally lacked chemotactic enhancing activity for C5a des Arg. Gc-globulin-depleted serum activated with zymosan also had significantly less chemotactic activity than control- (sham-depleted) activated serum. Finally, radioiodinated C5a or C5a des Arg formed a 1:1 complex with purified Gc-globulin when analyzed by gel filtration chromatography. These results indicate that Gc-globulin is the major chemotactic enhancing factor in serum and may function as an up-regulator of the chemotactic activity of C5-derived peptides.

Role of group-specific component (vitamin D binding protein) in clearance of actin from the circulation in the rabbit

The possible role of group specific component (Gc) (vitamin D-binding protein) in the clearance of cellular actin entering the circulation was examined with 125I-labeled Gc and actin injected into a rabbit model. Although filamentous F-actin is depolymerized primarily by plasma gelsolin, greater than or equal to 90% 125I-actin injected in either monomeric G- or F-form became complexed eventually with Gc (1:1 molar ratio). Clearance of Gc complexes was much faster (greater than 90% within 5 h) than that of native Gc (t1/2 = 17.2 h). Nephrectomy did not significantly alter the clearance of either Gc or actin. Since Gc complexes are dramatically increased in situations of tissue necrosis such as in fulminant hepatic failure, the current results suggest a crucial role for Gc in sequestration and clearance of released cellular actin.

Diminished serum Gc (vitamin D-binding protein) levels and increased Gc:G-actin complexes in a hamster model of fulminant hepatic necrosis

Evidence for increased plasma levels of complexes containing Gc (vitamin D-binding protein) and cellular actin has been previously reported during fulminant hepatic necrosis in man. In order to study this process in more detail, we produced liver injury in hamsters using increasing doses of acetaminophen, with serial collection of sera for up to 168 hr after acetaminophen injection. Hamster Gc was purified using a three-step procedure and was shown to resemble closely human Gc. Polyclonal antihamster Gc was prepared and used in rocket immunoelectrophoresis and radial immunodiffusion studies for quantitation of total serum Gc and the percentage of Gc complexed with actin. Serum Gc levels were depressed in animals having liver damage, and the extent of depression 42 hr after acetaminophen correlated with the extent of elevation of AST. The proportion of the total Gc that was present in the complexed form increased in relation to the severity of the liver disease. In serial studies, diminution in Gc level preceded the rise in AST and increase in the percent complexed. These changes closely resemble observations in man and suggest that the hamster-acetaminophen hepatotoxicity model may be of value in further study of interactions of Gc with intracellular actin components and its role in actin homeostasis in conditions of massive tissue necrosis.

The metabolism and mechanism of action of 1,25-dihydroxyvitamin D3

Much has been learned about the formation of the active metabolite of vitamin D3, 1,25-dihydroxyvitamin D3. Information concerning its formation and catabolism has allowed a clear understanding of factors involved in the maintenance of plasma concentrations of the hormone. The effects of 1,25-dihydroxyvitamin D3 on calcium transporting cells in the intestine are marked and well defined. The tissue (intestinal tissue) is easily isolated and manipulated and hence, this is an ideal tissue in which to examine the mechanism of divalent cation transport. The mechanism by which 1,25-dihydroxyvitamin D3 brings about this effect should help in understanding sterol hormone action.

Calcium metabolism in post-menopausal women

To investigate some parameters involved in postmenopausal calcium metabolism we have measured FSH, LH, estradiol (E2), parathyroid hormone (PTH) calcitonin (CT), 25-hydroxy-vitamin D3 (25-OH-D3), total calcium (CaT) and ionic calcium (Ca++) serum levels in 20 healthy postmenopausal women and 20 premenopausal women. The results reported show that the decrease of estradiol levels are associated with a significant decrease in 25-OH-D3 serum levels, possibly as result of a lower concentration of vitamin D binding protein, which is extremely sensitive to changes in oestrogen levels. The PTH levels were similar in both groups studied, which might be explained together with increased ionic calcium levels in postmenopausal women, by decreased parathyroid sensitivity to the blocking action of Ca++.

Altered configuration of Gc on the plasma membrane of transformed and malignant human B lymphocytes

Normal human peripheral blood B cells exhibit strong membrane fluorescence for Gc (vitamin D-binding protein), and this protein can form a close spatial relationship with integral membrane immunoglobulin (mIg) with evidence of codistribution in the lipid bilayer. In contrast, fluorescence for both Gc and mIg has been found in this study to be weak or absent in several B lymphoblastoid cell lines and in chronic lymphocytic leukemia B cells. Moreover, the comobility of these components, where detectable, was also impaired. In abnormal B cells, the intensity of membrane fluorescence for Gc was substantially increased after crosslinking of mIg with antibody, and the latter was also associated with increased specific radioiodination of Gc by lactoperioxidase. These results indicate that Gc can apparently become displaced under certain circumstances within or through the lipid bilayer. The altered content or membrane topography of Gc in such abnormal B cells might be associated with impaired expression and mobility of mIg.